With the recent increasing scope of microcomputer applications in various fields, there have appeared such weaving machines or looms that are equipped with a microcomputer which is used to control their operation. It is known to those skilled in the art that such microcomputer-controlled looms have advantages in that: (1) Production of inferior fabrics due to erroneous machine operation or malfunctioning of stop motion can be forestalled; (2) Loom maintenance can be facilitated greatly thanks to improvement in detection of abnormalities and in locating cause of any trouble associated with loom's control system; and (3) Microcomputer programming can make possible versatile capabilities of the loom and ease of the programming improves the control flexibility.
The use of a microcomputer in a loom can realize special control features that had been practically impossible with conventionally-controlled looms. The present invention refers to one such control feature in a loom, i.e., a control method by which loom's time-controlled operating system is brought to a stop at a predetermined position thereof when its motor is turned off with application of a brake because of a break in weft or warp yarn or occurrence of any abnormal situation in the loom. The predetermined position denotes a predetermined crank angle of crankshaft of the loom which is driven to rotate by the motor and the rotation of which governs the operating cycle of the time-controlled system of the loom.
It cannot be ensured, however, that the loom is brought to a stop at said predetermined crank angle by turning off the motor with simultaneous application of the brake which is operatively connected to the motor. It is because a constant braking force cannot be maintained at all times for a long period of service of the brake due to various influencing factors such as progressively increasing wear in the brake. If the loom fails to be stopped at the predetermined position after turning off the motor and application of the brake in response to a signal due to a break in either weft or warp yarn, the loom will be placed where it is inconvenient for the yarn breakage to be remedied. With an air-jet loom, it may be brought to a stop where air as the medium for weft picking is kept in an undesirable discharged state in spite that the loom is at a halt. In the event of such failure in stopping the loom at said predetermined position, manual adjustment should be performed by an operator so as to move the loom to the predetermined stop position.
However, the use of a microcomputer has made it possible to provide a control feature by which the loom can be stopped at a predetermined crank angle, thus dispensing with the above troublesome and time-consuming manual adjustment. U.S. patent application Ser. No. 367,959, the details of which will be described in later part hereof, discloses a control method for such a purpose. This method, which is carried out in a loom wherein the position where brake is applied for stopping of the loom is so adjusted that it may be stopped correctly at a predetermined crank angle, comprises the steps of detecting and storing the deviation of the actual stop position from said predetermined crank angle caused during just the previous braking operation, executing arithmetic processing operation for compensation for the current braking position on the basis of data regarding said deviation of the actual stop position during the previous braking operation, applying brake when the position determined through said compensation is reached by the loom, and detecting and storing the deviation of the actual stop position from said predetermined crank angle during the current braking operation for providing data for similar compensation for the braking position in braking operation that follows.
According to this prior art method, compensation is thus provided automatically in such a way that the loom may be stopped at the predetermined position, thereby the machine operator being released from troubles associated with monitoring the loom for its stop position and laborious, time-consuming manual adjustment. On the other hand, however, provision of the above automatic compensation rather poses a serious problem in that, depending upon fabrics to be formed, the purpose itself of the control method may not be accomplished. The problem is derived from the fact that the load imposed on the loom during each operating cycle or rotation thereof varies depending upon the kind of fabric texture to be formed. Though the lenght of time required for one pick in forming a plain-woven fabric is kept substantially constant, the time in weaving, for example, a corduroy varies in a specific way. It is because the load or the resistance in forming a shed in weaving operation changes from time to time according to the kind of texture of fabric to be produced. In view of such a phenomenon in weaving operation, the above-mentioned prior art method, according to which the position of current brake application is determined from the data of deviation of the actual stop position from the predetermined crank angle during the previous brake application, offer a problematic disadvantage. That is, if brake is applied currently at a position which corresponds to the maximum shedding load on the basis of stored data obtained at a position where the shedding load was the minimum, or vice versa, the stored data will not perform its intended function of compensating correctly for the position of current brake application, but adversely affect the control by amplifying an error in compensation. Thus, the proposed control method which is designed to realize accurate stopping of a loom at a predetermined position thereof eventually poses a problem in that the accuracy can be no more ensured if there takes place variation in shedding load which is determined by the type of fabric texture.